Stable solutions of optical brighteners

ABSTRACT

A stable aqueous solution comprising 
     (a) 5-25% by weight of an optical brightening agent of formula I ##STR1## in which R 1  to R 9 , X and A.sup.⊖  are defined in the specification 
     (b) 5-70% by weight of an organic monobasic acid or a mixture of organic monobasic acids selected from formic, acetic, propionic, butyric, glycollic and lactic acids, 
     (c) 0-45% by weight citric acid 
     (d) 5-55% by weight water 
     the total amount of organic acids present being at least 40% by weight of the total composition, and the total amount of components a, b, c and d being at least 90% of the total solution.

This application is a continuation-in-part of my copending application Ser. No. 230,547, filed Feb. 2, 1981 and now abandoned.

This invention relates to stable aqueous solutions of certain benzimidazole optical brighteners.

The invention provides a stable aqueous solution comprising

(a) 5-25% by weight of an optical brightening agent of formula I ##STR2## in which X is N or CR₅, A.sup.⊖ is an anion and (1) when X is N:

R₁, R₂ and R₄ are hydrogen

R₃ is C₁₋₄ alkoxy, unsubstituted or monosubstituted by phenyl or (C₁₋₄ alkoxy)carbonyl;

one of R₆ and R₇ is hydrogen or methyl, the other being hydrogen, and R₆ and R₇ are in the 3- and 4-position respectively,

R₈ is C₁₋₄ alkyl unsubstituted or monosubstituted by phenyl or (C₁₋₄ alkoxy)carbonyl, and

R₉ is C₁₋₄ alkyl, or

(2) when X is CR₅, R₅ is hydrogen, C₁₋₄ alkyl, phenyl or phenyl substituted by methyl and/or methoxy;

R₁ is hydrogen, halogen, C₁₋₄ alkyl, C₁₋₄ alkoxy or together with R₂ forms a fused benzene ring

R₂ is hydrogen, halogen, C₁₋₄ alkyl, C₁₋₄ alkoxy, --COOR, --CONRR or --SO₂ R', in which each R independently is H or C₁₋₄ alkyl and R' is --OH, C₁₋₄ alkyl, C₁₋₄ alkoxy, or --NRR;

or together with R₁ or R₃ forms a fused benzene ring;

R₃ is hydrogen, halogen, C₁₋₄ alkyl, C₁₋₄ alkoxy or together with R₂ or R₄ forms a fused benzene ring

R₄ is hydrogen, halogen, C₁₋₄ alkyl, C₁₋₄ alkoxy or together with R₃ forms a fused benzene ring;

R₆ is hydrogen, halogen, C₁₋₄ alkyl, C₁₋₄ alkoxy, phenyl, (C₁₋₄ alkyl)sulphonyl or phenylsulphonyl;

R₇ is hydrogen, halogen, C₁₋₄ alkyl or C₁₋₄ alkoxy;

R₈ is C₁₋₄ alkyl unsubstituted or substituted by phenyl; C₂₋₄ hydroxyalkyl; cyanoethyl; phenyl unsubstituted or monosubstituted by halogen, C₁₋₄ alkyl or C₁₋₄ alkoxy; or C₄₋₈ cycloalkyl;

and R₉ is C₁₋₄ alkyl unsubstituted or substituted by phenyl, C₂₋₄ hydroxyalkyl, (C₁₋₄ alkoxy)-C₂₋₄ alkyl, --CH₂ CN, --CH₂ CONH₂ or --CH₂ --COOR" where R" is C₁₋₄ alkyl,

(b) 5-70% by weight of an organic monobasic acid or a mixture of organic monobasic acids selected from formic, acetic, propionic, butyric, glycollic and lactic acids,

(c) 0-45% by weight citric acid

(d) 5-55% by weight water

the total amount of organic acids present being at least 40% by weight, preferably 45-65% by weight of the total composition.

Preferably 10-45% citric acid is present.

Preferably the total amount of components a, b, c and d is at least 90% of the total solution. More preferably the total amount of components a, b, c and d is 95%, most preferably the total amount of components a, b, c and d is 97%.

Preferably substantially the only solvents present are components b, c and d.

Preferred compounds of formula I in which X is N are those of formula I' ##STR3## in which R₃ ' is methoxy or (C₁₋₂ alkoxy)carbonylmethoxy

A.sup.⊖, R₆ and R₇ are as defined above,

R₈ ' is C₁₋₂ alkyl, unsubstituted or monosubstituted by phenyl or (C₁₋₄ alkoxy)carbonyl, and

R₉ ' is methyl or ethyl.

Particularly preferred is the compound of formula I' in which R₃ ' is methoxy, R₆ =R₇ =H, and R₈ '=R₉ '=methyl, particularly the salt form in which A.sup.⊖ is a halide or CH₃ SO₄.sup.⊖ anion or mixtures thereof. The term `halogen` used herein means F, Cl or Br, and `halide` means F.sup.⊖, Cl.sup.⊖ or Br.sup.⊖.

Preferred compounds of formula I in which X is CR₅ are those of formula I" ##STR4## in which R₁ " and R₂ " are each hydrogen or together form a fused benzene ring

R₃ " is hydrogen, methoxy or methyl

R₅ " is hydrogen or methyl

R₆ " is hydrogen, methyl, methoxy, chlorine or methylsulphonyl

R₈ " is methyl, phenyl or benzyl

and R₉ " is methyl or benzyl.

Of the compounds of formula I' and I", those of formula I' are preferred.

Component (b) is preferably formic, acetic, glycollic or lactic acid, or mixtures thereof. Acetic acid, glycollic acid and mixtures thereof are particularly preferred.

Suitable compositions contain 7-20% by weight of component (a) and 10-30% by weight of component (b) and 25-40% by weight of component (c) or 45-65% by weight of component (b) and no component (c); the former type being especially suitable.

The compositions of the invention may contain minor amounts of additional components, for example scented materials such as pine oil to mask any unpleasant odour from the organic acids.

The optical brighteners of formula I are known, and their preparation is described for example in German Offenlegungsschrift 2 733 439 and Swiss Pat. No. 593 967.

The compositions of the invention may be prepared in conventional manner by stirring the components together, e.g. at room temperature, until a homogeneous solution results.

The resulting compositions are useful as aqueous concentrates which may be diluted as required to give an aqueous treatment bath for the optical brightening of textile fibres, particularly of polyacrylonitrile. The compositions are stable, that is, they do not deposit any solid material on storage for up to several months at temperatures between 0° C. and 45° C.

The following Examples, in which all parts and percentages are by weight, illustrate the invention.

EXAMPLE 1

150 Parts of the optical brightener of formula ##STR5## were stirred at 20° C. with 250 parts of water and 600 parts of glacial acetic acid, to give a clear pale yellow solution, stable at 0° C., ambient temperature and 45° C. for at least 12 months.

EXAMPLE 2

150 Parts of the optical brightener of Example 1 were stirred at 20° C. with 314 parts water, 50 parts glacial acetic acid, 300 parts anhydrous citric acid and 186 parts of 70% wt. aqueous glycollic acid until a clear pale yellow solution was obtained having the following composition (% by wt.)

(a) optical brightener 15%

(b) monobasic acids 18% (acetic acid 5%, glycollic acid 13%)

(c) citric acid 30%

(d) water 37%.

The composition is stable at 0° C., ambient temperature and 45° C. for at least 12 months, and has very little odour.

EXAMPLE 3

150 Parts of the optical brightener of formula ##STR6## were stirred at 20° C. with 250 parts water, 100 parts glacial acetic acid, 300 parts anhydrous citric acid and 200 parts 70% glycollic acid, to give a clear pale yellow liquid stable at 0° C. for at least 6 months and having the following composition: (% by wt.)

(a) optical brightener 15%

(b) monobasic acids 24% (acetic acid 10%, glycollic acid 14%)

(c) citric acid 30%

(d) water 31%.

EXAMPLE 4

150 Parts of the optical brightener of formula ##STR7## were stirred at 20° C. with 250 parts water, 300 parts citric acid and 300 parts 70% glycollic acid to give a pale yellow odourless solution, stable at 0° C. for at least 6 months and having the composition

(a) optical brightener 15%

(b) glycollic acid 21%

(c) citric acid 30%

(d) water 34%.

EXAMPLE 5

A solution the same as that of Example 3 was formulated except that the optical brightener of formula ##STR8## was used instead of the optical brightener of Example 3. A pale yellow solution with very little odour and stable at 0° C. for at least 6 months was obtained.

EXAMPLE 6

A solution the same as that of Example 3 was formulated except that the optical brightener of formula ##STR9## was used instead of the optical brightener of Example 3.

EXAMPLE 7

A solution the same as that of Example 1 was formulated except that the optical brightener of formula ##STR10## was used instead of the optical brightener of Example 1. 

What is claimed is:
 1. A stable aqueous solution comprising(a) 5-25% by weight of an optical brightening agent of formula I ##STR11## in which A.sup.⊖ is an anion,R₃ is C₁₋₄ alkoxy, unsubstituted or monosubstituted by phenyl or by (C₁₋₄ alkoxy)carbonyl; one of R₆ and R₇ is hydrogen or methyl and the other is hydrogen; R₈ is C₁₋₄ alkyl unsubstituted or monosubstituted by phenyl or by (C₁₋₄ alkoxy)carbonyl, and R₉ is C₁₋₄ alkyl, (b) 5-70% by weight of an organic monobasic acid or a mixture of organic monobasic acids selected from formic, acetic, propionic, butyric, glycollic and lactic acids, (c) 10-45% by weight citric acid, (d) 5-55% by weight water,the total amount of organic acids present being at least 40% by weight of the total composition, and the total amount of components a, b, c and d being at least 90% of the total solution.
 2. A solution as claimed in claim 1 in which component (a) is an optical brightening agent of formula ##STR12## in which R₃ ' is methoxy or C₁₋₂ alkoxy carbonylR₈ ' is C₁₋₂ alkyl, unsubstituted or monosubstituted by phenyl or by C₁₋₄ alkoxy)carbonyl and R₉ ' is methyl or ethyl.
 3. A solution as claimed in claim 2 in which in component (a) R₃ ' is methoxy, R₆ and R₇ are hydrogen and R₈ ' and R₉ ' are methyl.
 4. A solution according to claim 1 in which A.sup.⊖ is halide or CH₃ SO₄.sup.⊖ anion.
 5. A solution according to claim 1 in which component (b) is formic, acetic, glycollic or lactic acid or a mixture thereof.
 6. A solution according to claim 5 in which component (b) is acetic or glycollic acid or a mixture thereof.
 7. A solution according to claim 1 in which the total amount of organic acids present is from 45-65% by weight of the total composition.
 8. A solution according to claim 2 containing 7 to 20% component (a), 10 to 30% component (b) and 25 to 40% component (c).
 9. A solution according to claim 8 wherein component (b) is acetic or glycollic acid or a mixture thereof.
 10. A solution according to claim 3 containing 7 to 20% component (a), 10 to 30% component (b) and 25 to 40% component (c).
 11. A solution according to claim 10 wherein component (b) is acetic or glycollic acid or a mixture thereof.
 12. A solution according to claim 1 wherein components (b), (c) and (d) are substantially the only solvents.
 13. A solution according to claim 2 in which the total amount of organic acids present is from 45-65% by weight of the total composition.
 14. A solution according to claim 8 in which the total amount of organic acids present is from 45-65% by weight of the total composition.
 15. A solution according to claim 2 wherein A.sup.⊖ is a halide or CH₃ SO₄.sup.⊖ anion.
 16. A solution according to claim 8 wherein A.sup.⊖ is a halide or CH₃ SO₄.sup.⊖ anion.
 17. A solution according to claim 9 wherein A.sup.⊖ is a halide or CH₃ SO₄.sup.⊖ anion.
 18. A solution according to claim 3 wherein components (b), (c) and (d) are substantially the only solvents.
 19. A solution according to claim 6 wherein components (b), (c) and (d) are substantially the only solvents.
 20. A solution according to claim 1 in which the amount of component (a) is 7-20%, the amount of component (b) is 10-30% and the amount of component (c) is 25 to 40%.
 21. A solution according to claim 20 wherein components (b), (c) and (d) are substantially the only solvents.
 22. A solution according to claim 8 wherein components (b), (c) and (d) are substantially the only solvents. 